05/04/18: Drupal CMS PECL YAML Parser PHP Object Injection

Threat Summary

Overview

A remote command execution vulnerability exists in the PECL YAML parser used in Drupal CMS. This vulnerability is present in versions 8.8.3 and below. An attacker is able to inject command execution payloads via crafted serialized requests, resulting in the ability to run arbitrary PHP objects on the target host. A valid, authenticated session cookie of at least administrator privilege is required for successful exploitation of this vulnerability.

Exploitation

Stages

The attacker send an HTTP POST request to a /configuration/single/import with the “import” parameter containing a PHP command injection payload.

The injected payload is parsed by Drupal’s YAML parser via unsafe usage and subsequently injected if the payload contains a valid PHP object.

Prerequisites

This vulnerability is present in Drupal Core versions 8.8.3 and below.

Alert Logic Coverage

Alert Logic® has evaluated its customer base for exposure to the exploit and has developed signatures for mitigating the threat depending on the security service in place.

The Network-Based Intrusion Detection System (IDS) has been updated with the new signatures for this exploit when detected via Alert Logic Threat Manager™. If this signature is detected, an incident is generated in the Alert Logic console.